Development of a low-temperature sintered dielectric material derived from Li 2 MgSiO 4 (LMS) for low-temperature cofired ceramic (LTCC) application is discussed in this paper. The LMS ceramics were prepared by the solid-state ceramic route. The calcination and sintering temperatures of LMS were optimized at 8501C/4 h and 12501C/2 h, respectively, for the best density and dielectric properties. The crystal structure and microstructure of the ceramic were studied by the X-ray diffraction and scanning electron microscopic methods. The microwave dielectric properties of the ceramic were measured by the cavity perturbation method. The LMS sintered at 12501C/2 h had e r 5 5.1 and tan d 5 5.2 Â 10 À4 at 8 GHz. The sintering temperature of LMS is lowered from 12501C/2 h to 8501C/2 h by the addition of both lithium borosilicate (LBS) and lithium magnesium zinc borosilicate (LMZBS) glasses. LMS mixed with 1 wt% LBS sintered at 9251C/2 h had e r 5 5.5 and tan d 5 7 Â 10 À5 at 8 GHz. Two weight percent LMZBS mixed with LMS sintered at 8751C/2 h had e r 5 5.9 and tan d 5 6.7 Â 10 À5 at 8 GHz.
Cerium oxide (CeO 2 ) filled polytetrafluoroethylene (PTFE) composites prepared by powder processing technique for microwave substrate application is presented in this paper. The PTFE is used as the matrix and the dispersion of CeO 2 in the composite is varied up to 0.6 by volume fraction, and the dielectric properties were studied at 1 MHz and microwave frequencies. The relative permittivity and dielectric loss increased with increase in CeO 2 content. For 0.6 volume fraction loading of the ceramic, the composite has e r of 5 and tan d of 0.0064 at 7 GHz. Different theoretical approaches have been employed to predict the effective permittivity of composite systems and the results were compared with that of experimental data. The serial mixing model shows good correlation with the experimental results.
were added to CeO 2 powder. The crystal structure of the ceramic-glass composites was studied by X-ray diffraction, microstructure by scanning electron microscopy, and phase composition using the energy-dispersive X-ray analysis technique. The microwave dielectric properties such as relative permittivity (e r ), quality factor (Q u xf), and coefficient of temperature variation of resonant frequency (s f ) of the ceramics have been measured in the frequency range 4-6 GHz. Addition of B 2 O 3 and Bi 2 O 3 -ZnO-B 2 O 3 -SiO 2 lowered the sintering temperature of ceria to about 9001C. The 20 wt% B 2 O 3 and 10 wt% Bi 2 O 3 -ZnO-B 2 O 3 -SiO 2 -added CeO 2 and sintered at 9001 and 9501C showed: Q u xf 5 24 200 and 12 000 GHz, e r 5 13.2 and 22.4, and s f 5 À46 and -57.2 ppm/1C, respectively.
Polytetrafluroethylene (PTFE) composites filled with CeO 2 were prepared by powder processing technique. The PTFE is used as the matrix and the loading fraction of CeO 2 in the composite varied up to 0.6 volume fraction. The thermal conductivity and coefficient of thermal expansion were studied in relation to filler concentration. The thermal conductivity increased and coefficient of thermal expansion decreased with increase in CeO 2 content. For 0.6 volume fraction loading of the ceramic, the composite has a thermal conductivity of 3.1 W/m C and coefficient of thermal expansion 19.6 ppm/ C. Different theoretical approaches have been employed to predict the effective thermal conductivity and coefficient of thermal expansion of composite systems and the results were compared with the experimental data.
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